Atalk show host has just bought 10 new jokes. each night he tells some of the jokes. what is the largest number of nights on which you can tune in so that you never hear on one night at least all the jokes you heard on one of the other nights? (thus, for instance, it is acceptable that you hear jokes 1, 2, and 3 on one night, jokes 3 and 4 on another, and jokes 1, 2, and 4 on a third. it is not acceptable that you hear jokes 1 and 2 on one night and joke 2 on another night.)